Waveguide mode transformers



April 8, 1958 E. A. N. wHn'EHl-:AD Erm. 2,830,273

wAvEGuIDE Moms: TRANSFORMERS Y Filed May 1o. 1954 United States .Y atent WAYEGUIDE MGDE TRANSFORMERS Eric Arthur North Whitehead, St. Albans, and .lohn Alexander Christie Kinnear, Bromley, England, assignors to Elliott Brothers (London) Limited, London, England, y

This invention relates to improvements in waveguide mode transformers and is particularly concerned with the provision of waveguide mode transformers for transforming high-frequency electro-magnetic energyv propagated in a rectangular section waveguide in the H mode into energy propagated in the H11 mode in a circular section waveguide.

It is an object of the present invention to provide a waveguide mode transformer of the general character referred to above which shall be capable of operation for precision purposes without undesirably large reflection of the incident energy and which shall be capable of reproduction on a commercial scale without the use of complicated fixtures and without the employment of a large skilled labour force.

According to one feature of the present invention a waveguide mode transformer for transforming energy propagated inthe normal or H10 mode in a rectangular section waveguide into energy propagated in the H11 mode in a circular section waveguide comprises a ,transition section of a waveguide having a rectangular aperture at one end having dimensions corresponding to those of the rectangular section guide and a circular aperture at the other end having a diameter corresponding to that of the circular section waveguide, the two apertures having their edges contained in parallel planes and having their centre points located on the axis of the section, a passage extending towards the circular aperture from the rectangular aperture and of the same shape and crosssectional area as the latter and another passage extending towards the rectangular aperture from the circular aperture and having its wall arranged to constitute part of the surface of a frustum of a cone having a larger en-d the diameter of which is substantially equal to that of the circular aperture and a smaller end of a diameter substantially equal to the smaller dimension of the rectangular aperture, the axes of the two passages being in alignment and the walls of the two passages meeting along curved lines.

In a modiiicationof the waveguide mode transformer described in the preceding paragraph the transition section may be split longitudinally into two halves along the plane normal to the broadface of the rectangular passage and passing through the axis thereof, the two halves being displaced lengthwise relative to each other by a distance approximately equal to one quarter of the wavelength of the energy. 1

The invention also extends to a method of manufacturing a waveguide mode transformer according to either of the immediately preceding paragraphs,v which comprises forming the said other passage, extending towards the rectatngular aperture from the circular aperture, in a transition section of a waveguide having initially a passage therethrough of rectangular cross-section throughout its length, by removing part of the wall of the section by a machining or like operation.

In order that the invention may be more clearly un- ICC derstood two forms thereof will now be described by way of example with reference to the accompanying drawings in which:

Figure l is an elevation of the transition section of a waveguide taken from that end formed with the circular aperture;

Figure 2 is a section taken on the line II--II of Figure l; v

Figure 3 is a section taken on the line III-III of Figure 1, and

Figures 4 'and 5 correspond to Figures 2 and 3 and show a modification. 1

In the example illustrated in Figures 1, 2 and 3 the waveguide mode transformer comprises a thick-walled transition section 1 of a waveguide having at one` end a rectangular aperture 2 and at the other end a circular aperture 3.

edges contained in parallel planes and having their centre y points located on the axis of the section 1. The wall of the passage 5 constitutes part of the surface of a frustum of a cone (indicated in dotted lines in Figures 2 and 3), the diameter of the larger end of the frustum being substantially equal to that of the circular aperture 3 and the diameter of the smaller end thereof being substantially equal to the smaller dimension of the rectangular aperture 2. The Walls of the passages 4 and 5 meet along curved lines indicated at 6 and 7 in Figures 2 and 3 respectively.

The transition section 1 described has a taper extending from the rectangular section passage 4 to the larger diameter end of the passage 5 which produces a rate of increase in the cross-sectional area of the passage 4, 5 through the section 1 which is least when the deviation from the rectangular passage 4 first takes place. This reduces considerably the fraction of energy reflected by the transition section. l

The transition section 1 may be produced by cutting the passage 5 in a thick-walled waveguide section through which a rectangular passage corresponding to the passage 4 extends initially for the whole length thereof by cut- `ting away part of the wall thereof by a machining or reaming operation.

Alternatively the transition section 1 may be produced by the electro-deposition of copper or other conducting metal lon a suitably shaped mandrel.

In operation the section 1 is connected at the one end having the rectangular aperture to a waveguide having a correspondingly dimensioned rectangular passage therethrough and at the other end to a waveguide having a circular section passage therethrough corresponding in cross-sectional area to the aperture'3. High frequency` electromagnetic energy propagated in then'ormal or H10 mode through the rectangular section guide isV transformed by the transition section 1 into energy propagated in the H11 mode in the circular section guide and owing to the fact that the increase in cross-sectional area of the Y passage 4, 5 is least where the deviationfrom the rectangular passage 4 irst takes place the fraction of energy reected by the transition section is quite small.

The fraction of reflected energy may be considerably reduced by modifying the transition section 1 in the manner shown in Figures 3 and 4. In this modification, the transition section 1 of Figures 1, 2 and 3 is split along a plane normal to the broad face of the rectangular passage 4 and passing through the axis thereof into two halves 1a and 1b. The half 1a is seen in elevation in quarter of the wavelengthof the energy. Thev end faces of the two halves 1a and 1b forming the.trausition section are machinedflat by cutting away the: parts shownI in broken lines.

The modiedl arrangement functions in the same way as that described with reference to Figures 1, 2 and 3 butl has the additional advantage that any energy reilected from corresponding regions of the half sections 1a and 1b willrbe in anti-phase and will substantially nullifyfeach other. f

Thewall of the passage may form part ofthe surface' ofa volume of revolution which. departs slightly from a straight-sided frusturn of a coneinprder to reduce further the; fractionof"y energy reflected by the transition section.` This may-be achieved' by suitably shaping: the wall ofthepassage 5N wherevit intersects the passage 4, e. g. lbyeformingthe radiuson4 the wallv ofthe passage 5 at this location, so that the passages 5 and` 6 blend smoothlyitrto'eachA other; The marginal surface of the passageS'adjacent to the aperture 3 may also be curved or radiused aswill be' understood;

What we claim is:l

1. A` waveguidewmode transformer for transforming energy propagated in' thenormal or. H10 mode in a rectangular' section=waveguide into energy propagated in the Hin mode in aA circular section waveguide comprisinga transition section of` a waveguide having a rectangular apertureat one end having dimensions corresponding to thosemttheVv rectangular section guide and a circular aperture atithe otherend having a diameter corresponding to4 that: ofJ the circular section waveguide, the twoapertures having theirv edges contained in parallel planes and havingztheircentre points located on the axis of the section, a first passage extending towards the circular: aperture from-the rectangular aperture and of the same-shapeandcross-sectional area as the latter and a second passageextending towards the rectangular aperture frornfthe circular: aperturein axial alignment with said firstpassageand-havingits: wall arrange-d to constitute part of the `surface -ofa frustum of a cone having a larger end, theadiameter of which istsubstantially equal to that of the circular aperture anda smaller end of a diameter `substantially.equal` to the smaller dimension of therectangularf` aperture, each `wall of said first `passage meeting ther` wall ofsaidfrsecond, passage along a curved line containedin theiplan'eof said` wall of said rectangular, passage.v v

2. A waveguide mode transformer according to claim l wherein the. transition,.section` is split longitudinally intoztwor. halves. along; the; plannormal to the` broad. face of the rectangulartpassage. and passing, through. the` axis thereof; and thevtworhalves are displaced lengthwise relative to eachother by a distance. approximately equal to one yquarter ofthe wavelength of.;the energy.

3. A waveguide. Inode;V transformer for ,transforming energy propagatedinsthevnonnalior-Hio mode in a rectanfgular, sectiontwaveguideeinto. energyv propagated: in. the H11 model. in; a; circularzsection waveguideccmprising a,

transition section of a waveguide having a rectangular.

aperture at one end having-dimensions,corresponding to those of the rectangular` ,section` guide and acircular;

aperture at the other end having adiametencorrespond- 6 ing to that of the circular section waveguide, the two,

apertures having their edges contained in parallel planes .the section, a passage extending towards the circular aperture from the rectangular aperture and of the same shape andcross-sectional area as the latter and another passage extending towards the rectangular aperture from the circularV aperture and having that part ofits wall lying to one side of `a plane normal to the broader faces of the passageV extending from the rectangular aperture and containing the axis of the last-mentioned passage arranged to constitute part of the surface of a frustum of a cone and that part of its wall lying to theother side of said plane arrangedto constitute part of the. surface of a frustum of a similar cone displaced axially with respect to said firstY mentioned frustum by a distance approximately equal to one quarter ofthe,v wavelength of the energy, each of said frustums having a larger end the diameter of whichis. substantially equal, to thatof the circular aperture and asmaller end of a diameter. Substanz tially equal to rthe smaller dimension off the rectangular aperturegthe axes of said two passages being in alignf ment andthe walls of the two passages meeting along the curved lines.

4. A waveguide mode transformer for transforming energy propagated in the normal or H10 mode in a rectangular section waveguide. into energy propagated in the H11 mode in a circular section waveguide comprising a transition section of a waveguide having a rectangular aperture at one end having dimensions corresponding to those of the rectangular section guide and a circular aperture at the other end having a diameter corresponding to that of the circular waveguide, the twoapertures havingtheir, edges contained in parallel planes andhaving their centre points located on the axis of the section, a first passage bounded by two opposed broader faces and two opposed narrower faces and extending towards the circular aperture, said passage being of the same shape andv cross-sectional area as said rectangular aperture and a second passage extending towards the rectangular'aperture from the circular aperture in axial alignment with said rst passage and having a r'st part of its wall lying to one side of a plane containing the aligned axes of said passages and normal to the broader faces of said rst passage ararnged to constitute part of the surface of a frustrum of a cone and a second part of its wall lying to the other side of said plane arranged to constitute part of the surface of a frustrum of a similar cone each of said frustrums having a larger end the diameter' ofwhich is substantially equal to that of the circular aperture and` a smaller end of a diameter substantially equal to the smaller dimension of the rectangular aperture, each wall bounding said firstpassage to said one side ofl said planey meeting said tirst part of 'the wall of'saidsecond passagesaid second part of the wall of said secondpassage along a curvedline containedin.` the planetofl the respective wall `of'said first passage.

References Cited in the: tile-of. this; patent UNITED STATES' PATENTS 

